Standard Wireline Data Processing
IODP logging
contractor: LDEO
Hole: U0070A
Expedition:
344S
Location: Baffin Bay (Labrador Sea)
Latitude: 75°42' 21.8502 N
Longitude: 65° 43' 46.3183 W
Logging date:
Sea floor
depth (driller's):
603.5 m DRF
Sea floor
depth (logger's):
603 m WRF(FMS/GPIT/EDTC-B/HNGS Downlog)
Total
penetration: 906.6 m DRF (303.1 m DSF)
Total core
recovered: 63
% of cored section
Oldest sediment recovered: Late Turonian
Lithologies: Organic-rich carbonaceaous mudstones, siltstones and sandstones, and sandy mudstones.
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in September 2012.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
| 1. HRLA/HLDS/DSI/MSS/EDTC-B | Downlog
|
32 |
Invalid caliper and HLDS data
|
||
Uplog
|
32 |
||||
2. FMS/GPIT/EDTC-B/HNGS
|
Downlog
|
255.9 |
32 |
Depth reference |
|
Pass 1
|
47.1 |
254.7 |
Recorded open hole |
||
Pass 2
|
47.6 |
252.3 |
Recorded open hole |
Hole U0070A was reported to be in good condition for logging.
Due to the erratic and unpredictable nature of iceberg movement, it was decided to combine as many tools as possible in the first logging run, which consisted of the HRLA/HLDS/DSI/MSS/EDTC-B tool string (the DSI replacing the APS). The tool string reached a depth of 862 m WRF, about 40 m above total depth. After three unsuccessful attempts to go past this depth, an uplog was recorded. No repeat uplog pass was recorded, due to the uncertain timing and the need to run the FMS tool string as soon as possible. The FMS/GPIT/EDTC-B/HNGS tool string was run next. In order to reduce the possibility of complication in the drill pipe, the string was deployed without MCD centralizers, to 860 m WRF. A downlog and two uplog passes were recorded without incident.
The sea state was calm, thus no wireline heave compensator was used during the logging operations.
The depths in the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). Generally, discrepancies may exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from a 'bottom felt' depth in soft sediment.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 603 m WRF). The sea floor depth was determined by the step in gamma ray values at 603 m WRF observed on the FMS/GPIT/EDTC-B/HNGS downlog. This differs by 0.5 m from the sea floor depth given by the drillers (see above). The depth-shifted logs wee then depth-matched to the gamma ray log from the downlog of the FMS/GPIT/EDTC-B/HNGS tool string.
Depth matching is typically done in the following way. One log is chosen as reference (base) log (usually the total gamma ray log from the run with the greatest vertical extent and no sudden changes in cable speed), and then the features in the equivalent logs from the other runs are in turn matched to it. This matching is performed manually. The depth adjustments that were required to bring the match log in line with the base log are then applied to all the other logs from the same tool string.
Environmental
corrections. The HNGS
and HRLA data were corrected for hole size during the recording. The HLDS data were corrected for hole size during the
recording.
High-resolution
data. Bulk density
(HLDS) and neutron porosity (APS) data were recorded with sampling rates of 2.54 and
5.08 cm, respectively, in addition to the standard sampling rate of 15.24 cm.
The enhanced bulk density curve is the result of Schlumberger enhanced
processing technique performed on the MAXIS system onboard. While in normal
processing short-spacing data are smoothed to match the long-spacing one, in
enhanced processing they are reversed. In a situation where there is good
contact between the HLDS pad and the borehole wall (low-density correction) the
results are improved, because the short spacing has better vertical resolution.
Gamma Ray data from the HNGS and ETDC-B tools were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated with standard frequency in the P&S monopole, lower dipole and
Stoneley modes in both passes. The upper dipole was recorded in low frequency. The velocities were computed from acoustic slownesses. They are
generally of good quality.
The quality of
the data was assessed by checking against reasonable values for the logged
lithologies, by repeatability between different passes of the same tool, and by
correspondence between logs affected by the same formation property (e.g., the
resistivity log should show similar features to the sonic velocity log).
Gamma ray logs
recorded through bottom hole assembly (BHA) and drill pipe should be used only
qualitatively, because of the attenuation of the incoming signal. The
thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.
A wide
(>12") and/or irregular borehole affects most recordings, particularly
those that require eccentralization and a good contact with the borehole wall
(HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL) and by the FMS tool (C1 and C2). Hole conditions were
A null value of
-999.25 may replace invalid log values.
Additional information about the drilling and logging operations can be found in the expedition report. For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: tanzhuo@ldeo.columbia.edu
Gilles Guérin
Phone: 845-365-8671
E-mail: guerin@ldeo.columbia.edu